When an egg is being fertilized, if the sex chromosomes are XX, the resulting animal will be a girl and if the chromosomes are XY the animal will be a boy. As the embryo is developing, ovaries will develop in cases of XX chromosomes and testicles will develop in XY chromosomes. Sexual reversal is when the chromosomal sex and gonadal sex are different. This will occur only as XX sexual reversal and can present as the dog being an XX true hermaphrodite (the dog will have female chromosomes and ovaries and testicles, or XX male, which means the dog will have female chromosomes while having testicles.

Sexual reversal is when the chromosomal sex and the gonadal sex of a dog are different; resulting in a dog having XX chromosomes while having both ovaries and testicles or XX chromosomes and only testicles.

Dogs with sexual reversal are infertile; therefore, your dog will not come into heat and will not be able to breed. You may notice that they have chronic irritation in their genital area. An XX true hermaphrodite will have ovaries and testicles while and XX male will have female chromosomes and testicles.

Types 

A few types of disorders of sexual development can occur in dogs. These include:

Known also as abnormality of chromosome differentiation, this is when rather than inheriting the usual XX or XY chromosomes, the dog inherits an atypical set. This can lead to Trisomy with an XXX or XXY or monosomy (one chromosome) X0. If a dog inherits two full chromosome sets (XX/XX or XX/XY) chimerism occurs.

A dog with this condition will have the typical male chromosomes, however the sex organs often do not develop as is typical. The dog may have ovarian tissue or an incomplete uterus. This condition is inherited and known to occur in Miniature Schnauzers.

A dog will have an XX chromosome set and can have sex organs that are both male and female and may or may not be complete. The condition has been seen in 28 breeds. This may occur as a result of environmental factors.

Also called cryptorchidism, this is when the testes of your dog are kept within his body. This may occur as a result of a chromosomal differentiation abnormality or as an individual occurrence. As time passes the testes can shrink and develop cancer.

Sex reversal is an autosomal recessive trait in the following breeds:

The condition also occurs in other breeds, however how it is inherited in those has not been confirmed.

Upon your veterinarian conducting an examination of your dog (whether a regular physical exam or if a dog presents as infertile) should he notice any abnormalities (like clitoral enlargement or an atypical penis) he might suspect a sexual development disorder. In order to make a diagnosis, your veterinarian will have to evaluate your dog’s internal and external sex organs and will send a blood sample for the chromosomes to be identified.

In cases of sexual reversal, your veterinarian will typically recommend that you spay or neuter your dog. Any abnormal tissue or retained testes should be removed. While your dog undergoes surgery, your veterinarian will likely remove an enlarged clitoris or abnormal penis as this will resolve pain or discomfort that your dog is experiencing in the genital area. For males that have a urethra in an atypical location, penile reconstruction surgery may be necessary.

Your dog’s recovery will depend upon his exact anatomy and the surgery he undergoes. In most cases, surgery will be like that of a spaying procedure. He will likely stay overnight at the hospital after his surgery and may be given pain medication. If any incisions were made, you will have to keep them clean and avoid them getting wet. Your dog’s activities should be limited for two or more weeks after his surgery. A follow up appointment will likely be necessary so that your veterinarian can see how your dog is recovering and stitches may need to be removed. In cases where surgery is not possible, for example if the health of your dog is poor, cream and medication will likely be recommended for relief from pain and irritation of your dog’s genitals.